Manufacture of ultrafilter membranes



MANUFACTURE OF ULTRAFILTER MEMBRANES Filed Aug. 30, 1923 Patented July16, 1929.

JACQUES DIJ'CLAUX,

OF PARIS, FRANCE.

MANUFACTURE OF ULTRAFILTER IEHBRAN ES.

Application filed August a0, 192;, serum no.

It is well known that membranes called ultra-filters comprisingcellulose'estcr films, have been used for some .years in scientificresearch laboratories. Several processes for. 6 their preparation havebeen described, but

these processes, which are suitable for laboratories, are too costly ortoo complicated to be of industrial application. They are not suited foruse in preparing for instance, 10 several hundred square metres ofultra-filter membrane, as it is necessary to do in industrialoperations.

The invention has for its object a process'for the production of thesemembranes in large quantities. This process hasthe advantage of beingparticularly economical owing to the fact that most of the solvent usedfor dissolving the cellulose ester can be recovered and used over again.The invention also includes certain improved membrances of the typelater described.

-According to this invention I form the cellulose ester filmsconstituting the ultrafilter on an unrolling strip of smooth cloth 2which is guided by rollers so as to dipfirst into a solution ofcellulose ester and subsequently into a coagulating liquid.

Referring to the appended drawing illustrating diagrammatically, as anexample, an apparatus for carrying out the process, the object of theinvention. i

The membrane, of cellulose ester and particularly of nitro cellulose, isforced upon a strip of cloth of any length, carried onroller's. Startingfrom a first storage roll a, the band dips first into a trough 6containing the solution of. cellulose ester or collodion, then it passesupon a guiding roller 0 and issues vertically'from the trough, carrying.by adhesion a certain quantity of collodion. At a certain distanceabove the trough, the strip of cloth, which has begun to dry, meets asystem of rollers d and e which guide it through a vat f full of acoagulating liquid, for instance, water, in which it proceeds for awhile. It emerges from it completely hardened and freed from most of thesolvent and is rolled up upon a last roll In the example illustrated onthe drawing, the strip passes only once in the 'vat filled with thecoagulating liquid. It is evident, however, that it is possible, bymeans of other rollers, to lengthen its path in this liquid to ensureits more thorough washing.

The single vat may also be replaced by sev- 660,178, and in FrauoeSeptember 11, m2.

eral successive vats, with. a methodical eirculation' of coagulatinliquid.

The s eed of trans ation must be sufli- 'ciently s ow for the collodioncarried awa by the strip of cloth to be solidified before arriving atthe roller d or elseit might stick to the latter. For greater security,

this rolle'r may be covered with'cloth, blotting paper or any otherporous substance mpregnated with the coagulating solution; in thismanner, adhesion is .cqmpletely avo ded, providedthat the solutionimpregnatmg the roller is frequently renewed.

The recovery of the solvent of the cellulose ester may be effected intwo ways. A first portion of this solvent evaporates durmg. the passageof the cloth between the collodion trough b and the roller d. Thevapours being heavier than air, fall .vertically; 1t 1s suflicient tosurround this part of the apparatus with a kind of casingand to collectat the lower portion the air loaded with vapours. Another portion of thesol-- vent is carried by the clothand is found dissolved in thecoagulating liquid, from which 1t can be extract (1. N

' It is possible to add to the machine so constructed an arrangementpermitting the control of the uniformity of the membranes. It

suifices for this to add a coloring matter to the liquid contained inthe coagulation vat.

Variations in the textureo r in the thickness of the filter membranewill then be represented by difierences in coloration which are at onceperceptible. I

In the method of manufacture of ultrafilter membranesfwhich has justbeen descrlbed, the strip of cloth acts merely as su port of thecellulose ester film which .is t e filtering element that is to say thefilm is supported in andspans the open mesh of the weave. The passage ofthis. strip of cloth 1n the collodion trough has simply for its objectthe impregnation of the cloth. It may be replaced by any otherarrangement conducive to the same result; for instance, the impregnationmay be obtained in causing, by means. of a nozzle, the collodion to flowon the cloth in a jet or thin film, either on both sides or on one sideonly.

Before passing into the machine which impregnates it with collodion, thecloth strip may receive a preparation adaptedto mo ify its filteringproperties; it may .for instance; be n oistened'with water ora solutionhaving for its purpose to-modify later on the filtering properties ofthe cellulose ester film.

the impregnated cloth is immersed in a coagulating bath.

2. The art of making ultra filter-membranes which comprises passingcloth through a solution of nitrocellulose of a consistency that willadhere to the cloth and fill the mesh thereof, removing the cloth fromsaid solution, permitting solvent to evaporate until the nitrocellulosecoating has solidified and the impregnated cloth does not adhere to aroller moistened with a coagulant for said nitrocellulose solution, andpassing said cloth throu h a coagulating solution.

3. The art of making ultra-filter membranes which comprises passingcloth through a solution of nitrocellulose of. a consistency that willadhere to the cloth and fill the mesh thereof, removing the impregnatedcloth from said solution, permitting solvent to evaporate until thenitrocellulose coating has solidified and the impregnated cloth does notadhere to a roller moistened with Water, and passing said cloth throughwater until the nitrocellulosecoating has completely hardened.

- In'testimony that I claim the foregoing as my invention, I have signedmy name.

' JACQUES DUCLAUX.

